A high electron mobility transistor (HEMT) is a type of field effect transistor (FET) in which a heterojunction is generally formed between two semiconductor materials having different bandgaps. In HEMTs, high mobility charge carriers are generally generated using, for example, a heterojunction of a highly-doped wide bandgap n-type donor-supply layer and a non-doped narrow bandgap channel layer. Current in a HEMT is generally confined to a very narrow channel at the junction, and flows between source and drain terminals, the current being controlled by a voltage applied to a gate terminal.
In general, a transistor may be classified as a depletion mode transistor or an enhancement mode transistor. In various applications, it may be desirable to have an enhancement mode switch device having a pinch-off voltage greater than 1 volt (V) and a relatively high maximum current density.